We have continued our studies on the biosynthesis, regulation, and function of polyamines in Saccharomyces cerevisiae. Our major effort during the past year has been on studying ornithine decarboxylase, the first step in the biosynthetic pathway for polyamines in yeast. We are studying the mechanisms of control in this system as a model for the eukaryotic enzyme, which has been of special interest because it increases very rapidly under conditions of rapid growth and differentiation. We have been studying five problems related to this enzyme: (1) purification of the enzyme; (2) regulatory control of enzymatic activity; (3) genetics of the enzyme; (4) development of methods to facilitate isolation of clones carrying the gene; and (5) physiologic affects of polyamine deprivation. (1) Procedures have been developed for the purification of a stable form of an 86,000 Mr protein, which is secondarily converted by proteolytic enzymes to a 68,000 Mr and a 35,000 Mr form. The enzyme has been shown to be a glycoprotein. (2) The enzyme loses activity after growth in the presence of polyamines; no obvious protein degradation is involved and the regulation is by a putative post-translational modification. (3) We have shown that all of the spe10 mutants, which lack ornithine decarboxylase activitiy, are located in the same genetic locus. It is still uncertain if this defect is in a regulatory or a structural gene. (4) A screening technique has been developed to select for strains that might have a recombinant plasmid carrying the gene for ornithine decarboxylase (or other genes in the polyamine pathway). Banks of recombinant plasmids have been constructed. (5) We have also been using the various mutants that we previously described to study the physiologic effect of polyamine deprivation. We have found that aminedeficient cells arrest in a budded stage, similar to cell division cycle mutants.